Hi Jon, (if anyone doesn't like my helping someone on an amplifier/antenna
question, just use the delete key now!)
You bring up some interesting questions we all face.
I too would like to know what amount of "lowpass filtering value" is lost
when the impedance is not 50 ohms on the output. Is 2:1 or 3:1 still "good".
Then of course what is "good"?
I try to avoid using the tuner as much as possible. Just one more thing to
tune up (and destroy!).
I have basically resonant antennas for 40-10 (Force 12 C4XL) with three
exceptions:
12M/17M about 3.5:1 (the antenna works pretty good here but is a free result
of the CCR design).
40M on SSB, the antenna is tuned for CW. SWR can get up to 3:1 at the high
end.
Forunately my amplifier is a Henry 3K Premier with PI-L output. The PI-L
affords an extra degree of filtering as opposed to a PI design. I simply
tune the amp into these loads. Full power, no problems. I also use a Henry
low pass filter between the wattmeter and antenna, grounded with one inch
braid 4 feet long to my ground rods.
I am currently using an open wire fed inverted vee about 170 feet long, apex
at 70 feet for 80/75M. I can use it on 160M too but prefer to shunt feed the
tower.
This configuration (even tried varying lengths of feedline) puts quite a
strain on my feeble tuners (MFJ 989C, and Tokyo HY-Power HC-2000). My
solution will be to cut my new dipole for 3650 KHz and live with the
resulting SWR of about 3:1 at 3500 or 3800 KHz. Another possibility would be
to cut the antenna for 3800 KHz and use a tuner in only one spot, 3500 KHz.
This way I could just switch the tuner out of line and just switch it back
in for 3500 KHz and it will be tuned correctly. All bets are off if you need
to use the tuner in two or more bands! I would suspect the 3:1 or 5:1 SWR
would be easier to handle for the tuner than the possible 20:1 + SWR
presented by the open wire feedline at some frequencies.
Indeed my BIRD 43 is not accurate with the higher SWR but can be counted on
for relative fwd/ref power.
73, Dan Magro W7RF, (President WARC 1999, member SCDXC, SCCC)
Manufacturers Rep & Distributor for HENRY RF Power Amplifiers.
www.radiodan.com <http://www.radiodan.com> ??? RFpower@radiodan.com
<mailto:RFpower@radiodan.com> A trip to our web site is worth the click!
> -----Original Message-----
> From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
> Behalf Of Jon Ogden
> Sent: Monday, March 29, 1999 2:40 PM
> To: km1h@juno.com; amps@contesting.com
> Subject: Re: [AMPS] Amp opinion/infomation requested ASAP!!
>
>
>
> >I do not own an antenna tuner and have no need for another device of
> >questionable efficiency.
>
> I understand why folks do this, especially after having some arcing
> problems in my tuner on 80m during the WPX contest (had to do an
> emergency cap repair on my output cap in the tuner - a plate had some
> serious meltdown!). However, there are a couple of reasons why I like
> the concept of a tuner. For one, it gives an additional layer of
> harmonic filtering. Second, low pass filters are designed to have their
> lowpass response based on a 50 Ohm input and output and third, power
> meters are pretty much designed the same way.
>
> So how do you get around this? Having a power meter on a non-50 Ohm
> system probably isn't a big deal. But I think it could be a big deal
> with the lowpass filter. Or do you not run a lowpass filter and count on
> the harmonic suppression in the tank circuit to be good enough?
>
> 73,
>
> Jon
> KE9NA
>
>
> --------------------------------------------------------------------------
> Jon Ogden
>
> jono@enteract.com
> www.qsl.net/ke9na
>
> "A life lived in fear is a life half lived."
>
>
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